1. Field of the invention
The invention relates to a receiver for television and teletext signals, including a teletext decoder which provides the possibility of searching a plurality of teletext pages and storing them in a page memory. The receiver also includes a page number memory in which the desired teletext page numbers are preferably stored when the receiver is switched off.
Such a receiver may be, for example a television receiver or a video recorder.
2. Description of the prior art
A television receiver or video recorder including a teletext decoder is generally provided with a (remote) control system with which the user can switch on the teletext operating state and with which he can subsequently search pages by generating the desired page numbers with the aid of numbered keys. The instructions given by the user are applied to a control circuit which interprets these instructions and passes them on to a teletext decoder. Inter alia, the page with the page number stated can be searched by the decoder, stored in a page memory and displayed on a display screen. Since the teletext pages are cyclically transmitted and since such a cycle lasts a relevant period, it may take some time before the desired page appears on the display screen.
By taking certain measures, this waiting time can be reduced considerably. For example, it is proposed in reference [1] to store the pages transmitted in the cycle in their order of reception in a memory. After a page has been requested by the user, the decoder searches for the presence of this page in the page memory. Large memories are required for this purpose because a considerable reduction of the waiting time can only be realised if the page memory comprises at least an essential number of the teletext pages transmitted in the cycle. Such large memories are, however, relatively expensive.
To meet this problem, teletext decoders have been developed which can search and store a limited but relevant number of pages and which comprise registers stating the page numbers to be searched. An example of such a decoder has been described in reference [2]. In these types of teletext decoders, which will hereinafter be referred to as multipage teletext decoders, the waiting time reduction is achieved by filling the registers as well as possible in conformity with the pages to be actually displayed. To this end it is proposed in reference [3] to store a series of page numbers stated by the user in a page number memory for a later successive display of these pages. Such a television receiver is notably very satisfactory if the number of pages which the multipage teletext decoder can store is relatively small, for example smaller than the number of stored page numbers. In fact, the waiting time is effectively reduced because the multipage teletext decoder searches, for example, the first four pages of the pages qualifying for display. A non-volatile page number memory is preferably used so that the stored page numbers are also preserved after the receiver is switched off.
The said receiver has the drawback that the user must explicitly store the numbers of the pages to be displayed in the page number memory. This means that he enters the numbers intentionally in a desired sequence and that he generates special control instructions, for example terminating a page number by means of a store key. The receiver also has the drawback that the page number memory may get filled up whereafter the further entry of page numbers is no longer possible. Furthermore the pages are displayed in their sequence of storage so that for the display of a given desired page a plurality of pages which is irrelevant at that moment must be glanced through by operating a recall key. The ease of operation of this known receiver is therefore found to be a drawback in practice.